Advanced evolution mobile broadband communication systems, such as those being developed to conform to the 3GPP LTE-Advanced and IEEE 802.16m communications standards, require scalable bandwidth from 5 MHz to 100 MHz. In other words, channel bandwidths will be required which are well beyond the 20 MHz bandwidth currently standardized for LTE. LTE-Advanced is also required to be backwards compatible to LTE, primarily focused on low-mobility users in order to reach ITU-Advanced's requirement on data rates, further increase voice over IP (Internet Protocol) capacity, further improves cell edge data rates and improve self configuration of the communications network. It is necessary to develop a scheme for mapping a MAC (media access control) layer to a physical layer.
One proposed MAC-to-physical layer mapping scheme currently being considered by the 3GPP for inclusion in the LTE-Advanced standards consists of multiple identical signal processing chains. In each chain, a transport block is channel coded, rate matched, scrambled, modulated and precoded. The precoded symbols corresponding to each transport block are then mapped to resource element (RE) in the allocated resource blocks (RB) of a particular component carrier. However, even though a number of different component carriers are used to transmit transport block data, no improvement in frequency diversity over current LTE standards is achieved since data from each transport block is transmitted on one component carrier only.
In order to achieve such a frequency diversity improvement, another MAC-to-physical layer mapping scheme has been proposed. In this scheme, resource blocks associated with each coded, rate matched and modulated transport block are distributed amongst a number of available component carriers. However, the link adaptation capability of this scheme is relatively poor because only one type of modulation scheme can be applied for each transport block for each Transmission Time Interval (TTI) regardless of which component carrier the symbols from each transport block were mapped to.